Coincidence amplifier



April 1, 19 2 H. D. FARNSWORTH COINCIDENCE AMPLIFIER Filed Feb. 27, 1948 //v l/EN TOR I HUGH 0 FAR/vswoRTH Patented Apr. 1, 1952 FFICE COINCIDENCE AMPLIFIER Hugh D. Farnsworth, Berkeley, Calif., assignor to the United States of America as represented by the United States Atomic Energy Commission Application February 27, 1948, Serial No. 11,605

Claims. (Cl. 250-27) This invention relates to a two channel amplifier circuit arranged to provide a single output and more particularly to aicoincidence amplifier.

In present day research projects for determining the properties of atomic particles, it is necessary to count the quantity of such particles traveling in a given direction. For accurate determinations it is necessary to eliminate those particles which are due to scattering. It is proposed by this invention to devise an electrical circuit to operate with ionization chambers to eliminate inaccuracy in particle counting due to random and scattered particles.

It is therefore an object of the invention to provide a coincidence amplifier.

Another object of the invention is to provide a multichannel amplifier, the output signals of which are applied to .a mixer in such a manner that a signal has to appear simultaneously at the output of each channel before a signal will appear at the output of the mixer.

A further object of the invention is to provide a new and improved circuit for determining the quantity of high speed particles traveling in a predetermined direction.

A still further object of the invention is to provide a coincidence amplifier comprising a trigger circuit, a first blocking grid oscillator to charge a condenser and to operate a second blocking grid oscillator, which in turn causes the condenser to discharge, forming a voltage of variable duration in response to each input' pulse of voltage.

in the following description and claims considered together with the accompanying drawing in which:

There is illustrated a schematic wiring diagram embodying the invention.

Referring to the drawing in detail, there is shown a first amplifier channel 18, a second amplifier channel 28, and a mixer 36. The two amplifier channels 18 and 28 are identical in all respects and the following description will deal only with the first amplifier channel I), as being representative. A plug 4! which is externally connected to a power supply (not shown) furnishes a first and second voltage or positive polarity 42 and 43 to both amplifier channels, a ground connection 44 to both amplifier channels, and a separate negative voltage 46 and 41 to the two amplifier channels l8 and 20 respectively. An input plug 5| is connected to a coupling condenser 52 which, in turn, is connected to Other objects and advantages will be apparent 'througha coupling condenser 69.

the control grid of a pentode type tube 53. Th

control grid of this tube 53 is connected to aresistor 54 which is connected to the adjustable portion of a potentiometer 56 and a condenser 51. One end of the potentiometer 55 is connected to the open end of the condenser 51 and tothe ground connection 44, while the other end of the potentiometer 56 is connected to a resistor 58 which is, in turn, connected to the negative voltage 46. The cathode of the tube 53 is connected to the ground connection 44 through a parallel network comprising a resistor 59 and a condenser 8l. The screen grid of the tube 53is connected to the ground connection 44 through a bypass condenser 62 and is further connected to the common junction of two resistors 63 and B4 of a resistancevoltage divider connected between the positive voltage 42 and the ground connection 44. The suppressor grid of the tube 53 is held at ground potential by the lead 66 which electrically connects them. A further connection of the tube 53 is made from the anode to the posi-.- tive voltage 42 through a dropping resistor 81 and to the control grid of a pentode type tube 68 The control grid of the tube 68 is connected to the ground connection 44 through a resistor H.. Further connections of the tube 68 are as follows: the cathode is connected to the ground connection 44 through a resistor 12, the screen is connected to the common junction of two resistors 13 and I4 which divide the voltage between the positive voltage 42 and the ground connection 44.and is further connected to the ground connection 44 through a by-pass condenser 16, the suppressor grid is connected to the ground connection 44 by means of a lead 11, and the anode is connected to the positive voltage 42 through a dropping resistor l8 and further to the ground connection 44 through a variable condenser 19. Theanode of the tube 68 is still further connectedto the control grid of a pentode type tube 8| through a coupling condenser 82. The control grid of the tube 8| is also connected to a resistor 83 whichis connected to the junction of two resistors 84 and 86 comprising a voltage divider between the negative voltage 46 and the ground connection 4.4. The junction between the two resistors 84 and is connected to the ground connection 44 through a condenser 81. Other connections of the tube 8| are as follows: the screen grid isconnectedto the positive voltage 42 by the lead 88, the suppressor grid is connected to the cathode by a lead 89 and further to the ground connection 44 by the same lead, and the anode is connected-to through a by-pass condenser 93.

connection 44.

3 one terminal of the primary winding of a transformer 90 and to the anode of a pentode type tube 9|. The second terminal of the primary winding of the transformer 90 is connected to the positive voltage 43 through a dropping resistor 62 and is also connected to the ground connection 44 One terminal of the secondary winding of the transformer 99 is connected to the cathode of the tube 9I and the second terminal is connected to the control grid of the tube 9| through a coupling condenser 94. The control grid of the tube 9! is also connected to a resistor 95 which is, in turn, connected to the junction of two resistors 96 and 9?. These two resistors 96 and '9! are serially connected between the negative voltage 46 and the ground connection 44. The junction between the resistors 96 and 91 is connected to the cathode of the tube 9I through a blocking condenser 98. Other connections of the tube 9I are as follows: the anode is connected to the screen'grid and suppressor grid by a lead 99, and the cathode is connected to the ground connection 44 through multi-section delay line I04 through a coupling.

condenser I06. The control grid of triode A of of the tube I02 is connected to a resistor I01 which is, in turn, connected to the junction of two resistors I08 and I09 of a voltage divider between the negative voltage 46 and the ground The junction between the two resistors I08 and I09 is further connected to the ground connection 44 through a condenser III. The anode of triode A of this tube I02 is directly connected to the positive voltage 42 by means of a lead II2. A further connection of the tube l02'is made from the cathode to the ground connection 44 through a resistor H3 and a storage condenser II4. The delay line I04 comprises ten sections which are serially connected, each section comprising an inductance and a condenser .and the last section is terminated in a resistor H5. The junction between each of the ten sections of the delay line I04 is tapp d to a contact point on a selector switch II6, the variable element of which is connected to the control grid of 'a-pentode tube II'I through a serially connected coupling condenser IIS and current limiting resistor H9. The junction between the condenser are as follows: the screen grid is directly connected to the positive voltage 42 by a lead I26, the suppressorgrid is connected to the cathode and to the ground connection 44 by a lead I21.

'the anode is connected to one terminal of the primary winding of a transformer I28 and to the anode, screen grid, and suppressor grid of a pentode type tube I29. The other terminal of the primary winding of the transformer I28 is connected directly to the positive voltage 43 by a lead I3 I. One terminal of the secondary winding of this transformer I28 is directly connected to 'the cathode of the tube I29 by a lead I32 and the other terminal of the winding is connected to the control grid of the tube I29 through a coupling condenser I33. Further connections of 4 the tube I29 are as follows: the control grid is connected to a resistor I34 which, in turn, is connected to the cathode through a condenser I36 and to the junction of two resistors I31 and I38 comprising a voltage divider between the negative voltage 46 and the ground connection 44, and the cathode is connected to the ground connection 44 through a resistor I39. The cathode of the tube I29 is further connected to the control grid of triode B of the tube I02 through a coupling condenser I4I. Other connections of triode B of the tube I 02 are as follows: the control grid is connected to the negative voltage 46 through a biasing resistor I42, the cathode is connected to the junction of two resistors I43 and I44 which comprise a voltage divider between the negative voltage 46 and the ground connection 44, and the anode is connected to cathode of triode A of this tube. The junction between the resistors I43 and I44 is further connected to the ground connection 44 through a by-pass condenser I46; An output lead I46 is also connected to the anode of triode B of the tube I02 and serves as a coupling means for the signal of the first amplifier channel'I0. A similar output lead I41 serves as a coupling means for the signal of the second amplifier channel 20. The lead I46 is connected to the third grid of a multigrid type tube I48 through a coupling condenser I49 and the lead I4! is connected to the first grid of the tube I48 through a coupling condenser I5 I. Other connections of this tube I49 are as follows: the cathode is directly connected to the ground connection 44 by a lead I52 and to the fifth grid, the first grid is connected to a resistor I53 which is connected to the junction of two resistors I54 and I56 which comprise a voltage divider between the negative voltage 46 and the ground connection 44, the second and fourth grids are connected together and further connected to the junction between two resistors I51 and I 58 which comprise a voltage divider between the positive voltage 42 and the ground connection 44, and the anode is connected to the positive voltage 42 through a dropping resistor I59. An output lead I6I is connected to the anode of the tube I48 through a coupling condenser I62. The output lead I6I is further connected to an output plug I63. The ground connection 44 is connected to a second output plug I64. Further, a plug I66 serves as an input terminal for the signal to the second amplifier channel 20.

Now referring to the operation of the device, the connections of which have been described in detail above. With the input plugs 5Iand I66 connected to ionization chambers to be usedin coincidence counting of particles, a particle entering the chambers will cause an input pulse to appear at the plugs and thus impress a signal on the input circuits of the two amplifier channels I0 and 20. Since both amplifier channels I0 and 20 are identical, the operation of the first channel I0 will be dealt with in detail hereinbelow.

A positive pulse of voltage at the input plug 5I of the amplifier channel I0 impresses a positive pulse of voltage at the control grid of the tube 53. =Since the tubes 53 and 68 are interconnected and properly biased to form' a pulse forming amplifier circuit with the tube 53 normally nonconductive and the tube 68 normally conductive,rthe positive pulse of voltage causes the tube 53 to conduct, thereby resulting in the tube 68 becoming nonconductive. As the current ceases to flow through the tube 68 the anode voltage of this tube increases toward the value of the positive voltage 42, which increase in voltage is coupled to the control grid of the tube SI. Now, since the tubes 8| and SI are interconnected and properly biased to form a trigger circuit and a blocking oscillator circuit, respectively, the positive voltage pulse impressed at the control grid of the tube 8I results in the formation of a sharp positive voltage pulse being generated at the cathode of the tube 9| which is coupled to the control grid of triodeA of the tube I02 and to the delay line I04. The aforementioned voltage pulse at the cathode of the tube SI is in phase with the input pulse at the plug 5I. The triode A of the tube 8 2 is connected asa cathode follower; therefore, the condenser I I4 in its cathode circuit becomes charged positively during the time the tube conducts. Since the same positive pulse of voltage which results in the Charging of the condenser H4 is coupled to the delay line, a positive pulse of voltage can be impressed at the input of a second trigger circuit and blocking oscillator circuit comprising, the tubes II! and I29, respectively, at a'later"time. The delay time is adjustable by means of the switch IIB which can be used to determine the number of sections of the delay line I04 to be utilized in the circuit. Thus, at a time later than that of the positive pulse of voltage at the cathode of the tube iii, a second positive pulse of voltage is formed at the cathode of the tube I29. Since the cathode of the tube I29 is coupled to the control grid of triode B' of the tube I02 through the condenser MI and the anode of this triode B is connected to the corn denser II4, the anode of triode B is maintained positive by the charge on the condenser H4 and triode B conducts during the time its control grid is positive, thereby discharging the condenser H4. Thus, a positive voltage of variable duration is present across the condenser II4 and is available at the output lead MS of the amplifier channel I0.

:Similarly, a positive voltage of variable duration is available at the output lead I47 of the amplifier channel 20 in response to a positive input pulse of voltage at the input plug I66.

Now, with the leads I46 and I41 connected to the third and first grids of the mixer tube I48, it is seen that a voltage pulse will appear across the output plugs I53 and I 64 only at such times as both grids are positive. Thus a coincidence circuit has been developed, whereby it is possible to trace the paths of charged particles and to count the number of these particles in any desired path with greater accuracy.

It is further seen that for still greater accuracy it is possible to connect two or more of these devices in cascade with the ionization chambers along the desired path and to mix the output signals in such a manner that only under the condition of a particle passing through all of the chambers, will an output signal from the final mixer stage be generated. It is to be noted that, although the means for mixing theoutput pulses of the amplifier channels has been shown in detail on the drawing, there are several methods by which the desired result can be obtained.

For coincidence counting a counter can be connected to the plugs I63 and I64. The output voltage at the plugs I63 and IE4 can also be used to initiate operation of a secondary circuit if desired.

While the salient features of the invention have been described in detail with respect to one embodiment, it will, of course, be apparent that numerous modifications may be made within the spirit and' scope of the invention audit is therefore not desired to limit the invention to the exact details shown except insofar as they may be defined in the following claims.

What is claimed is:

1.In a coincidence counting device the combination comprising at least two amplifier channels each having at least a first oscillator, means for initiating operation of said first oscillator in response to an input pulse of voltage, means for storing energy during operation of said first oscillator, a second oscillator responsive to the output voltage of said first oscillator at a predeterminedlater time, means responsive to the output of said second oscillator to discharge said stored energy, and means responsive to the output voltages of said amplifier channels whereby a single output of voltage is obtained when the output pulses of voltage of said amplifier channels occur within a predetermined period of time.

2. In a coincidence counting device the combination comprising at least two amplifier channels each having at least a pulse forming amplifier circuit operated by input pulses of voltage, a first oscillator responsive to the output voltage of said amplifier, a condenser for storing energy during operation of said first oscillator, a second oscillator responsive to the output voltage of said first oscillator at a predetermined later time, means responsive to the output of said second oscillator to discharge said condenser, and means responsive to the output voltages of said amplifier channels whereby a single output of voltage is obtained when the output pulses of voltage of said amplifier channels occur within a predetermined period of time.

3. In a pulse forming circuit the combination comprising a pulse forming amplifier circuit operated by input pulses of voltage, a first oscillator responsive to the output voltage of said amplifier, means for storing energy during operation of said first oscillator, a second oscillator responsive to the output voltage of said first oscillator at a predetermined later time, and means responsive to the output of said second oscillator to discharge said stored energy whereby a pulse of voltage of predetermined duration is formed across said energy storing means.

4. In a pulse forming circuit the combination comprising a pulse forming amplifier circuit operated by input pulses of voltage, a first oscillator responsive to the output of said amplifier, a condenser for storing energy during operation of said first oscillator, a second oscillator responsive to the output voltage of said first oscillator at a predetermined later time, and means responsive to the output of said second oscillator to discharge said condenser whereby a pulse of voltage of predetermined duration is formed across said condenser.

5. In a coincidence counting device, the combination comprising at least two amplifier channels, each of said channels having a first oscillator connected to a source of voltage pulses, a first triode tube with its control grid coupled to an output of said first oscillator for charging a condenser in its cathode circuit each time said oscillator is activated, a delay line connected to said output of said oscillator, a second oscillator connected to said delay line for forming a pulse of voltage at a predetermined time later, and a second triode tube with its control grid connected to the output of said second oscillator and its anode connected to said condenser whereby said condenser is discharged each time said second 7 oscillator is activated forming a voltage of variable duration across said condenser, and means connected to said condenser of each channel for developing an output voltage only when said condensers are each charged.

HUGH D. FARNSWORTH.

REFERENCES CITED The following references are of record in the file of this patent:

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